I am in the process of swaping in a 383 and 200-4R tranny in my 77. I'm a weekend (and only part time at that) mechanic so this process has been going on for some time.

Anyway I have never attempted anything like this before so I am never quite sure when it comes to the odd things that pop up if it's normal but I got a problem now that can't be good.

I bolted the tranny and engine togeather outside the car and I noticed that when I bolted the converter to the flexplate it did not sit flat on the three flexplate mounting pads. It did not seem right but the flexplate looked straight to me so I bolted everything up.

The engine is now in the car and today I decided to have my wife crank the engine over while I took a look at the starter. I wanted to make sure everything lined up. The starters was fine but what I saw was the flexplate moving back and forth at least 3/16 of an inch as the engine cranked over. That can't be good. The crank is from a 400 and the flexplate is externally balanced. If that makes a difference.

All I can think of is the flexplate must have taken a smack during shipping. It's bent. At least I think it's bent and not the crank.

Is this OK because it's hard to believe this is OK. I'm thinking I will have to get a new flexplate. Can the flexplate be changed without pulling the engine? Anyone got any suggestions or advice on how to do this. I have the car on jackstands but I don't have much room underneath. I'm wondering if I can split the tranny from the block and slide it back enough to get my arm up there. I'm just bummed after seeing this today.

 

I'm a bit confused on that one since if you bolted the converter down tight, there should be no space between it and the mounting pads on the flex plate even if the plate was slightly bent. Hopefully you won't have to pull the works out again but if you do, you might want to drop the trans to get to it instead of pulling the motor.

 

sounds bent

 

When I bolted down the converter it all pulled in tight. The problem is when the engine rotates the flexplate flexs. It wobbles. Moves back and forth.

 

Maybe that's why they call it a FLEX Plate

Seriously though, unfortunately that sounds bent

 

It sounds like it's bent at the mounting flange. It needs to be replaced.

You can unbolt the engine from the transmission ( make sure BOTH are supported ) and remove/replace the flex plate.

If you purchased a new flexplate it should be returned for exchange or your money back. Good luck if you purchased it used. ( sorry )

Jeff

 

Another thought here. When you put the flexplate on the crank did it look ok? If you didn't notice the problem until you bolted the converter up, could one of the mounting tabs for the converter be bent? If so, the flexplate might bend when you bolt them together. May want to check that too before assuming it's the flexplate. Either way, it has to come apart to be changed...bummer.

 

To answer the questions above.

The converter tabs looked ok and sat flat on a bench. I don't think it's that.

The flex plate was used. I will have to buy another one. I have looked at Jegs and Summit and both have them from $59 up into the hundreds. I want a simple but sturdy one. Any reccomendations? The summit house brand looked like a good deal.

Remember I said I put in a 200-4R. The rear mount on this tranny is over the top of the cross member. I think I have to pull the cross member off the car to lower the rear of the tranny and then unbolt from the engine block. Is that the best approch or is there a better way? How far can you lower the rear of the engine without screwing up the motor mounts. I know I would have to watch for the distrubuter hitting. I don't have the front fan on yet so nothing will hit up there.

Any suggestions

 

Summit parts work well for me so that's what I would go with if you find that's the problem.
What you'll want to check before you pull the works is that the converter itself isn't wobbling. I've never heard it happen, but if the input shaft on the trans is bent, that would cause the wobbling you described too.
You're correct that you'll need to remove the crossmember to get the trans out.

 

Agreed, it sounds bent. There are other possibilities as well, but I think you'll need to pull the tranny to remove the flexplate and check it out.

A word of caution in flexplates & flywheels - if you do the math on the momentum that thing acquires spinning at 100 rev per sec (6000 rpm), it's easily enough to rip through a firewall and femurs if it fragments at any appreciable rpm. These "flywheel explosions" are not unheard of, so you'll want to be careful even with the lighter flexplate. My point: buy a new one. It's only money.

Good luck!

Dave

 

Point taken on the foot amputation.

Dropped the tranny today. Spun the converter still attached to the tranny and it looks to be running straight and true.

Unbolted the flexplate and it does not look as cockeyed as it looks when it was installed and rotating. I put it on a flat surface and it has a slight rock at spots but again nothing like it looked on the engine.

I hope to God almighty that the crank is not bent. Looking at the beef of that think it's hard to believe that could be bent. I won't rest easy until I have another plate bolted up and it looks to rotate true.

Anyone else ever have this problem?

 

I wonder if it is hanging up and not seating properly on the crank.

 

what if you put a dial indicator on the crankmating surface and turned it one revolution ?? that may alleviate or confirm some fears